digital audio to FCDEV3B

[Serg l]

Hi,
I'm looking for a way to connect FCDEV3B (given that it will be available
at some point) to an external system which is going to make and receive GSM
voice calls. The easy way would be to connect it via analog AUXI and AUXOP
interfaces available in Iota, however it would be a bit inefficient when
source and consumer of the audio is all digital.

I see that Iota is connected directly to LEAD SPI (DSP core). And also Iota
is driving the interface by sending 500kHz clock signal and VFS, when
bi-directional DX/DR serial transfer of 16-bit words is initiated. Do we
know if there is any way to intercept data transferred here and replace it
with encoded audio from/to the host system? I could not find any way to do
it from Calypso nor Iota side.
Alternatively it would be nice to be able to disconnect Iota VSP using a
jumper exposed on an external header and let an external system to
encode/decode data and implement SPI master hardware, which is available as
an FPGA IP as an example.

I checked an option to handle TCH data directly by bypassing the vocoder,
however I would like to take advantage of available hardware. Handling TCH
directly would be okay, but it will tax the host system resources and
require more strict UART data prioritization in order to keep codec data
flowing. Also for better compatibility we would need to implement more
codec variants including FR/HR and possibly AMR.